Thermal equilibrium

A ceramic tile in a pottery furnace has three black body panels in a line across the center.

The rectangles are ideal radiators/absorbers (black bodies). On the left the temperature of the panel containing the black body is slightly cooler than the surroundings. The black body absorbs slightly more radiation than it emits. In the center the panel is in thermal equilibrium - all surfaces emit as much radiation as they receive. On the right the panel is slightly hotter than the surroundings. The black body emits slightly more radiation.

The inside of a pottery furnace, when in thermal equilibrium, is a uniform orange - irrespective of what is in it.